The present invention relates to a modulator base of a modulator assembly for electrostatic voltmeters for use in electrophotographic processes. More particularly, the invention is directed to a modulator base having a defined configuration for construction of an improved modulator assembly and electrostatic voltmeter.
In an electrostatic imaging process, six stages are utilized to produce an archival quality image on a copy sheet, such as a page of plain paper. These steps are practiced upon and around a photoreceptor element (P/R), such as a photoreceptor belt or drum, hereinafter simply xe2x80x9cphotoreceptor.xe2x80x9d The imaging stages comprise: (1) photoreceptor charging, (2) image formation or exposure, (3) image development, (4) image transfer from the photoreceptor to a copy sheet, (5) fixing of the image on the copy sheet, and (6) restoring the photoreceptor. The process proceeds in a continuous loop and, if a color image is desired, steps (1), (2) and (3) are repeated in sequential stations around the photoreceptor for toner particles of black, magenta, yellow and cyan prior to completing steps (4) through (6) of image transfer, image fixing and restoring the photoreceptor surface to a clean and neutral state.
The second and third process steps of latent image formation on the photoreceptor and image development by applying a desired quantity of toner at a precise location on the photoreceptor latent image require accurate control of an electrostatic charge on the photoreceptor. This can be accomplished by electrostatic charge monitoring and a feedback loop. In particular, in a high speed image development process the toner particles are highly charged and coulomb forces are used to attach charged toner particles to a latent image on the photoreceptor. The magnitude and location of toner deposit is critical to a successful high speed electrophotographic process. Accordingly, accurate monitoring and modulation of an electrostatic field around the photoreceptor is essential. Electrostatic voltmeters, such as application specific integrated circuit electrostatic voltmeters, measure electrostatic fields or potential without current flow through the meter.
A typical electrostatic voltmeter includes a modulator assembly having a sensor electrode or probe and a modulator for modulating the electrostatic field that is being measured in relation to the sensor. The modulator assembly is the sensing element of the electrostatic voltmeter. Electrostatic voltmeters of this type are disclosed in U.S. Pat. No. 5,212,451 to Werner, issued May 18, 1993, and U.S. Pat. No. 5,489,850 to Werner et al., issued Feb. 6, 1996, both of which are assigned to the Xerox Corporation and are of common assignment with the subject application. The disclosures of these prior patents are hereby incorporated by reference as though set forth at length.
One approach to modulating an electrostatic field is to provide an electrostatic voltmeter modulator assembly having a vibratory beam with a device for interrupting the electrostatic voltage or simply xe2x80x9cchopper.xe2x80x9d The chopper oscillates when the vibratory beam is induced to vibrate by a magnetic driver, for example, causing the sensor electrode or probe to repeatedly couple and decouple with an external electrostatic field through a sensing aperture or window in the modulator assembly. Such an approach for modulating an electrostatic field is disclosed in the aforementioned prior U.S. Pat. No. 5,212,451 to Werner and in co-pending application Ser. No. 09/770,243 to Werner, titled xe2x80x9cSYSTEM FOR PURGING ELECTROSTATIC VOLTMETER MODULATOR ASSEMBLYxe2x80x9d, filed on the same date as the subject application, and assigned to the Xerox Corporation which is of common assignment with the subject application. The disclosure of the aforementioned co-pending application is hereby incorporated by reference as though set forth at length.
One problem with current electrostatic voltmeter modulator assemblies, in electrophotographic systems, is that reliable and accurate sensing of the electrostatic field requires the modulator and the modulator assembly to be accurately tooled and assembled. Consequently, manufacture and assembly costs of modulator assemblies tend to be high and performance and dependability of the electrostatic voltmeters are subject to variation based upon how well parameters of the modulator assemblies are controlled during manufacture and assembly. Accordingly, it would be desirable to provide a modulator base for an electrostatic voltmeter modulator assembly having a configuration which simplifies assembly, reduces manufacturing costs, and provides improved performance and robust functionality of the electrostatic voltmeter.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that prior art electrostatic voltmeter devices will admit to worthwhile improvement.
It is, therefore, a general object of the invention to provide an improved electrostatic voltmeter system, which will obviate or minimize difficulties of the type previously described.
It is another general object of the invention to provide an improved modulator assembly for an electrostatic voltmeter operable for providing a high level of photoreceptor voltage control for an electrophotographic process.
It is a specific object of the invention to provide an improved modulator assembly of an electrostatic voltmeter having a modulator base with accurate configuration to obtain improved operational reliability and performance of the electrostatic voltmeter.
It is another specific object of the invention to provide an improved electrostatic voltmeter modulator assembly having a modulator base which provides simplified assembly of the modulator assembly and electrostatic voltmeter.
It is another specific object of the invention to provide a modulator base for a modulator assembly of an electrostatic voltmeter whereby the modulator assembly is easy to manufacture and exhibits enhanced operational performance and impenetrability to contamination.
It is yet another specific object of the invention to provide an improved modulator base for a modulator assembly of an electrostatic voltmeter, which has an accurate configuration and fabricated with design features that ensure simplified and accurate construction and assembly of the modulator assembly and electrostatic voltmeter.
It is yet another specific object of the invention to provide an improved modulator base for a modulator assembly of an electrostatic voltmeter, which maximizes the possibility that critical mechanical and electronic parameters of the modulator assembly and electrostatic voltmeter will be advantageously controlled during manufacture and assembly.
To achieve at least some of the foregoing objects, the invention provides an electrostatic voltmeter having a modulator assembly for modulating and sensing an electrical field of an electrophotographic system. The electrostatic voltmeter includes a modulator base of the modulator assembly for mounting the modulator assembly in the electrostatic voltmeter. A vibratory beam is disposed in the base for modulating an electrical field by oscillating when a vibratory magnetic force is applied at one end of the beam. A sensor electrode is positioned at the other end of the beam for sensing an electrical field modulated by the vibratory beam. At least one reference mounting surface is provided on the modulator base for orienting and aligning the modulator assembly with respect to an electrical field of the electrophotographic system. The at least one reference mounting surface includes a first projection at one end of the modulator base for abutting against a mounting frame of the electrophotographic system so that an opposite end of the modulator base is located at a predetermined position with respect to the electrical field.
A chopper is provided at one end of the beam and the chopper and sensor electrode are situated at the end of the modulator base which is located at a predetermined position with respect to the electrical field. A second projection and a third projection at the one end of the modulator base abut against a base of the electrostatic voltmeter for positioning the modulator assembly in the electrostatic voltmeter. At least one air purge groove is positioned at a front end of the modulator base and, in a preferred embodiment of the present invention, comprises a pair of parallel grooves. A magnetic drive is provided in the modulator base for applying a magnetic force to one end of the vibratory beam. The magnetic drive has a magnet and a pair of beam mounting surfaces are provided in the modulator base for positioning the beam at a predetermined orientation with respect to the sensor electrode and the magnet.
Magnet reference surfaces in the modulator base, at opposite sides of the magnetic drive, lie in the same plane. The magnet is positioned in the modulator base such that a top end of the magnet, proximate to the vibratory beam, lies in the same plane as the magnet reference surfaces. At least two shielding areas are provided in the modulator base. A first shielding area is a floating shield for electrically shielding the sensor electrode and a second shielding area is a grounded shield for electrically shielding a magnetic drive area of the modulator base. The first shielding area includes slots adjacent opposite ends of the sensor electrode and the floating shield extends in the slots to electrically shield the sensor electrode. Alignment projections are situated on a bottom surface of the modulator base for aligning and retaining the modulator assembly in the electrostatic voltmeter.